Can A Receiver Flex?

[Ron J]

Had trouble posting in sporterizing, will try here. Anyway, it's a Mauser problem my brother and I can't figure out. He has a Brazilian 98, DWM, Berlin. He rebarreled with a .338 Shaw barrel, Dave Manson .338-06 reamer and checked with Forrester gages. He had lapped the lugs very little and has 95% fit on bottom lug and about 50% on top. All on one side of the ejector slot. There was about .0025" gap at the front shoulder when torqued to the inner. Shot 5 heavies to check for set back tied to a tire. The bolt comes up but stops and has to be slapped to open. Also, the primers backed out some. Fired 36 more rounds , some heavy, some light. The primers come out on the light loads and are flattened on the heavies. Z once explained the primer comes out first then the case stretches back around it. This makes sense (except for the first 5 which were heavy.) All cases were full length sized and are lengthening .005" when checking the datum with a Stoney Point gage. Figuring set back we checked with the head space gages and there was slightly more closing on the no go. Very slight. He pulled the barrel and there is a bright spot where the bottom lug rests, but no steps. Anyway, faced off .0015" from the tenon and torqued back on. Now it is just a touch away from closing on the go. We have a tight chamber. Shot 4 more light loads and the primers are coming out of all four. The first 2 shots the bolt opened, the second 2 had to be forced open again. He had marked where the gages stopped the bolt before and after rechecking, there is no change. Lastly, with the bolt stripped, when you pull back on it while opening, there is some kind of snap as the lugs start down the ramps. Same area as when it tightens when trying to open after firing.

Really confused. If you have a tight chamber, how do the primers back out? Why is the bolt hard to lift? Can the bolt move rearward or the recvr flex while firing and then come back and tighten against the case somehow?

I know this is long, but I'm trying to give you guys everything we see.

Thanks in advance for any help.

Ron

[z1r]

Generally speaking when you have low pressure load (light loads) and the primers back out its due to excess headspace. How did you check/set headspace? How did you chamber? Was it in the lathe or by hand on the receiver? Did you set headspace by taking measurements with a depth micrometer or just by closing the bolt on a gage?

 

Receivers can flex, especially mausers, but that is not likely the issue here. When you mention bolt lift I immediately think setback. Did you check for it? Usually what causes the hard to lift bolt is the fin or ridge left on the upper lug seat where the ejector slot is. This can also lead to false headspace readings.

[Ron J]

Chambering was done in a lathe. Chamber end was indicated in a four jaw chuck. The muzzle fits through the spindle and is indicated in a spider. Headspace was checked with the Forrester gages provided with the reamer. The reamer was held by a center in the tailstock and brought in by turning the hand wheel. It is checked with a depth mic until about .020" from complete. Then the recvr is screwed on with the bolt in it and the go gage in the chamber. The gap is measured between the recvr and the barrel shoulder. The recvr is taken off, gage taken out and the chuck is locked. Then the reamer is brought in just turning by hand with an indicator mounted on the tailstock to check how deep it's going. This is done and checked a couple times until the bolt just wants to close on the go gage. Then the barrel is torqued tight. This should be a low limit chamber if anything. When the barrel was taken back out, we did a visual for set back. Not that I'm totally familiar, but we don't see any. There's no protrusion of metal going into the slot. I know what that looks like, my Turk has it. The hard bolt lift is not at the start of lift, but when the lugs are starting to go down the angle cam surfaces. Just at that break.

[z1r]

Ok, did you weld on a new bolt handle? If so, did you notch the receiver? If so, does the notch by chance stop the rearward movement of the bolt. It is possibe, easy in fact, to not hav enough clearance in the notch so that the handle is actually arresting the rearward travel of the bolt and not the lugs. This will definitely lead to spring and can cause the symptoms you describe.

 

I usually chamber as you do except that if the distance from receiver ring to bolt face is .635" I chamber until the gage protrudes .633". That way when cinched up the bolt just closes on the go gage.

[Ron J]

I'm also thinking that something other than the lugs is "locating" the bolt. He did not weld on a handle, but did forge the original for scope use. Now that you mention it, the fiberglass stock he bought had the bolt notch in it and he had to put a bit of rearward bend in the handle to fit it. It could be touching at the inside corner somewhere on the recvr. We will look there next. We have checked and re-checked the chamber dimensions even comparing the gages to the cases. Everything is inside a few thousandths envelope. Something is incorrect elsewhere in the assembly.

I noticed in another post your officially in business. Congrats.

Ron

[z1r]

Thanks.

 

I would check the forged handle. The receiver or the stock could be keeping it from closing properly or "locating" the bolt as you said. I've seen it more than once. A lot of times people will lap their lugs before altering the bolt handle so they are making good contact. Then they alter the handle and assume the lugs are still making proper contact when they go to fit & chamber the barrel.

 

Let us know how it works out.

[Ron J]

The bolt handle appears to have enough clearance. The problem is starting to look like it's in the front recvr ring. When you open the bolt slowly, it "snaps" when the lugs come off the surfaces and start to head down the ramps. This is the same area where the bolt gets real hard to move after firing. During this "snap", the front end of the bolt jumps to the right side of the recvr. The extractor is off. If you hold a small screwdriver in the slot for the ring and put a little pressure on the bolt to the right side, this does not happen. We had a little tig welding done on the left side to fill some pits and now we are thinking something may be warped. The welder is good, we used an aluminum heat sink and rags, but he is not a gunsmith, either. If the C ring was ovaled, could the lugs force the bolt to the left when closing and maybe off the seats a little? I think the lugs are not seated when the gun goes off, springs backward, comes back on a .005" longer case with a protruding primer, and gets stuck in this "off" area. I just can't find why.

Ron

[Ron J]

We are narrowing this down, but certainly not finished. While dry firing, the shroud drops down. Out of the stock, this doesn't happen. I think the tang is getting drawn down and we're putting a pillar in it. This may explain why the upper lug only touches randomly. I've only messed with a couple of Mausers and I know the bolts are typically sloppy, but there just may be too much in this one. If you blue the lugs and just open and close using firing pin spring pressure, the upper lug is not rubbing. If you push back on a stripped bolt through the barrel it does. The snap we saw is the leading edge of the 3rd lug coming out off the recess. I put my Turk bolt in it and it does the same thing. I don't think it touches when closed though as the front camming pulls it forward. We stopped at 3AM Sunday morning and I went home. Had car repairs to do Sunday and just couldn't look at this thing anymore.

Bloodshot Ron.

[z1r]

Like I said, these things are hard to diagose without the action in front of you. There are a whole host of things that I look for automatically that just don't seem to come out when I have to type.

 

I don't know how much you've lapped the lugs but one of the ever present dangers is that if you remove enough material from the lugs the third lug may start to come into contact. Then, due to parts being interchanged, there is the chane that the third lug will contact even without lapping. This can and should be fixed.

 

When bedding a mauser you must be careful to assure that the receiver is bedded so that the receiver is not bent. Did you use screws when you bedded to tighten the action down?

 

It is normal for one of the lugs not to bear when you have the firng pin and trigger in. The sear will push up on the rear of the bolt causing it to tip. As soon as the pin is released the lug comes into battery though.

 

Inspect all the lug surfaces for small ridges, roughness, etc. Make sure the rear lug isn't contacting. I've had a few where it was.

 

Good luck.

[Ron J]

Thanks for all your help, Z. Just for s&g, we pulled the barrel, measured against an Argentina, took a couple thou off the tenon and screwed it in. It headspaced good so we shot it with the same loads that would bind up the other bolt. It shoots fine, bolt opens up easy and the head space didn't change. Whatever it is is in the front ring. Time to get back to more inspection and if that don't work, it's getting sent to your shop! We're either gonna learn alot or wave the white flag.

Thanks again, Ron

[z1r]

Thanks for all your help, Z. Just for s&g, we pulled the barrel, measured against an Argentina, took a couple thou off the tenon and screwed it in. It headspaced good so we shot it with the same loads that would bind up the other bolt. It shoots fine, bolt opens up easy and the head space didn't change. Whatever it is is in the front ring. Time to get back to more inspection and if that don't work, it's getting sent to your shop! We're either gonna learn alot or wave the white flag.

Thanks again, Ron

 

 

Well, if you can't get it to work, send it my way. I'll take care of you. Good luck!

 

-Mike

[peanut]

Walnut,

 

Did you solve the problem?

 

Hugh

[Ron J]

No. I have been putting about 11-12 hours a day in at work. Just come home, eat and read this forum a little before sacking out. I have the recvr while my brother is out of town. The barrel's out. Watching the boltface while you open the bolt, you can see the front of the bolt jump over to the extractor side just as the lugs get to where the ramps meet the flats. For what it's worth, if you slide a pc of ground flat stock along the bottom rails it lays flat. As you get to the front ring it rocks. My next move is going to try and fixture it vertical from a .700"+ shaft running through it, in a vee block. Maybe I can indicate it inside and see if it's twisted or warped from welding. I looked and felt inside a couple times for burrs or edges like Z recommended, but found nothing yet. Just not enough experience with Mausers, I guess.

Thanks for asking. I'll be sure to post if I find something.

[Ron J]

Walnut,

 

Did you solve the problem?

 

Hugh

 

Well here's what about 6 hours of playing around with this thing has proven. My .704" mandrel binds in spots. Not threading it in just pushing it in from the front. It marks the inner torque shoulder only on the bottom of the through hole. It touches the top of the hole that is part of the recoil lugs behind it. As though the front ring is heading upwards. Now a ground straightedge rocks when held against the bottom rail edge, but only on the thumbslot side. The "high" spot is about 2" behind the lug that hangs below the recvr. This is an area that was welded to fill pits. This along with we think we were pulling down a little on the rear tang when it was bedded.

I don't know...what do you guys think?

Ron

[donmarkey]

It is quite common in geha mauser shotguns to have the receiver bent that way. Also I have seen them bent front someone prying them out of the stock or twisted from barrel removal and install. Out of curiosity have you put a couple winding sticks on the bottom to see if it is twisted?

-Don

[Ron J]

It is quite common in geha mauser shotguns to have the receiver bent that way. Also I have seen them bent front someone prying them out of the stock or twisted from barrel removal and install. Out of curiosity have you put a couple winding sticks on the bat to see if it is twisted?

-Don

Hate to sound stupid, but what is "winding sticks on the bat"? I'm going to assume you mean how did we take the original barrel out. Before my brother retired from the fabricating shop he made some action wrenches in their toolroom. One each for Mauser LR, Model 70 Win and one more, I think for Ruger M77. They are almost identical to the ones Brownells sells. He practically fitted them to the shapes of the front rings. (We had to stone the inside a little to fit my Turk when we pulled it apart.) I'd be dam surprised if we twisted this recvr with it.

[donmarkey]

Sorry, I edited it, Some times I type too fast. I meant to say bottom. And even with proper tooling and precautions in your work, it's a surplus rifle so who else worked on it. If the bottom is square on one side and not the other, it is twisted.

-Don

[Ron J]

Well I'm just going to have to dream up a way to straighten it. Won't shoot like it is, so I can't screw it up! By the way Don, that stock really is looking good. And just what are winding sticks?

[donmarkey]

Well I'm just going to have to dream up a way to straighten it. Won't shoot like it is, so I can't screw it up! By the way Don, that stock really is looking good. And just what are winding sticks?

 

Thanks and winding sticks are basically 2 straightedges. You would place one at the front ring and one at the rear before the tang. And when you stand back and sight down with one in front of the other you will easily see any twist if the tops aren't parallel with each other.

-Don

 

[tinkerfive]

Well I'm just going to have to dream up a way to straighten it.

 

I have an idea!

 

If you had a flat bar the height and width of the locking lugs,

you could insert it in through the lug guides up to the point of

the twist.

 

With the ring secured in your action wrench you could put a

(pipe) wrench on the flat bar protruding from the rear of the action and twist.

 

 

[Ron J]

I was going in that direction except using the ID and a plug threaded in the front to match up to. Similar logic. The tough part about this is finding the exact part that is bent and focussing on it alone. There's not a lot of square surfaces to work from, but that is the beauty of them. Your method may show me more of what's cockeyed and where.

Thanks for the idea.

Ron

[peanut]

Ron,

 

Here's a thought. Put the receiver back on the facing mandrel, chuck it up in the lathe as if you were going to face it off, turn the receiver bottom so that it is facing you, lock the spindle. Mount an indicator on your tool post or carriage, and run the indicator across the length of the bottom of the reciever, both top and bottom of the bottom of the receiver. I know that sounds goofy. That should tell you if there is any canting that is not visible to the unaided eye. This may not give you the answer, but maybe it will help eliminate something that it is not. In any case I hope you find the solution.

 

Hugh

 

[z1r]

I've seen receiver with some slight warpage on them and none displayed the popping up of the bolt that you describe. Doesn't mean it couldn;t happen. About the only thing that could act on the bolt is the rear bolt lug. Think about it. There are other things that could cause your problem.

[Ron J]

I guess what I am thinking is that the front ring is tilited upward towards the front. When you open the bolt and it's cocking, spring pressure is pulling it rearward. I think only the bottom lug is contacting during the initial half of rise. Just as you reach this spot, it can start down the ramp and at that moment the top one is coming back and touching. It does also seem to be hitting the third lug right then. When you close the bolt it moves forward enough to not bear on the third lug. If I take enough stuff off to see clearly, it's hard to make it happen. I'm sure something else could cause this. The twist just happens to be the first thing I've been able to see that's not kosher.